An experimental dengue vaccine protected 100 percent of people when it was put to the test in a clinical trial, researchers reported Wednesday, a significant finding in the quest to battle a disease that infects an estimated 400 million people a year.
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The results of the dengue study were published in the journal Science Translational Medicine.
This helped researchers identify the vaccine’s effectiveness in people who had not been previously exposed to any strain of dengue.
A phase 3 trial of TV003 began on February 22 and is being conducted by the Butantan Institute in Brazil, Durbin said. In that climate, the human challenge model used to study TV003 gave researchers a way to safely demonstrate the vaccine’s efficacy on a small scale.
“Development of vaccines for dengue has been complicated, since disease can be caused by any of four dengue virus serotypes [strains]”, explained study author Dr. Beth Kirkpatrick, director of the Vaccine Testing Center in the department of medicine at the University of Vermont College of Medicine in Burlington. But despite the fact it triggers good antibody production, the protection the Sanofi vaccine offers is modest. Normally the efficacy of a new vaccine is tested in large studies in areas affected by the disease, but those kinds of studies can take up to 10 years and cost millions of dollars.
Leading dengue expert Dr. Scott Halstead applauded the use of this approach for this vaccine. In contrast, Dengvaxia could increase the risk of dengue disease among young children who have not been exposed to dengue virus before – a group that is similar to the USA population.
The TV003 vaccine was already found to be effective in preventing dengue 1, 3 and 4. First, they injected 21 volunteers with the experimental vaccine, and 20 other volunteers with a dummy vaccine.
According to Kirkpatrick, human challenge models have been used in the past to study other infectious diseases, including malaria, norovirus, influenza, cholera, Campylobacter and Shigella.
In addition, a vaccine against the Zika virus, a close relative of dengue, will most likely enter clinical trials this year. Not a single one of the vaccinated participants developed an infection by any measurement: virus circulating in the blood, rashes, or dips in white blood count.
Q: Can vaccine development ever get ahead of the next infectious threat? Forget mosquito bites. Volunteers let researchers inject them with the dengue virus in the name of science, and an experimental vaccine protected them.
The high prevalence of natural dengue infections in endemic areas means that many people have experienced infection at some point in the past and therefore may have immunity to the infecting serotype. Now, the World Health Organization has said that local Zika transmission has been reported in more than 50 countries or territories. After six months, they “challenged” those volunteers with a weakened strain of DEN-2, which causes only a mild infection, a slight rash, and a dip in white blood cell count.
Halstead said it made sense that the group started with dengue 2. This phenomenon is the reason that the first time a person is infected with dengue, he or she usually has a mild infection, but if that person is infected a second time with another of the four virus types, the existing antibodies aren’t up to the job; they actually help the virus infect cells rather than halt it in its tracks. Zika is racing across parts of Latin America and the Caribbean and could be associated with birth defects in the fetuses of pregnant women who become infected and may also be linked to adult cases of the neurological disorder Guillain-Barre.
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“We believe that a safe Zika human challenge model can be developed and would be instrumental in the acceleration of Zika vaccine development”, said Durbin, an associate professor at the Johns Hopkins Bloomberg School of Public Health in Baltimore. In previous human challenge trials with this modified virus, Dr. Whitehead and his coinvestigators established the virus dose that would cause all recipients to develop viremia-the presence of virus in the blood-and most to develop a mild rash.
